This invention relates to a form-fill-seal packaging machine. More particularly, this invention relates to a control device for the longitudinal sealer of such a packaging machine.
Such a packaging machine of the so-called vertical pillow type transports an elongated thermoplastic bag-making material (the "film") along the outer surface of a filling cylinder while bending it into a tubular form by means of a former and to seal the mutually overlapping side edges of the film by means of a longitudinal sealer and simultaneously both the top edge of the bag which has been filled and the bottom edge of the next bag to be filled by means of a transverse sealer. For the longitudinal sealing, a sealer employing a heat belt is commonly used.
A packaging machine of this type is usually operated without stopping except in the case of a trouble, transporting the film continuously. In the case of a packaging machine of the type forming a system with a weigher, the packaging machine serving as the "main" and the weigher serving as the "slave" such that the weigher will serve to supply articles to be packaged in response to a "ready" signal outputted from the packaging machine, the packaging machine may be designed to stop the transport of the film temporarily when no articles are supplied from the weigher for whatever reason and to remove the heater belt so as to separate it from the film. If no articles are supplied in the next cycle, however, the heater belt will heat the same portions of the film in preparation for the next packaging operation, thereby damaging the film and producing a defective bag.
If the mechanism for transporting the film and the heater belt are controlled so as to be activated together, however, the longitudinal sealing will not be effected sufficiently on the beginning portion of the film, again producing a defective bag which can easily break after transversely sealed.